U.S. patent number 5,107,834 [Application Number 07/647,658] was granted by the patent office on 1992-04-28 for low energy multiple shock defibrillation/cardioversion discharge technique and electrode configuration.
This patent grant is currently assigned to Cardiac Pacemakers, Inc.. Invention is credited to Roger W. Dahl, Paul A. Guse, Raymond E. Ideker, Douglas J. Lang, David K. Swanson.
United States Patent |
5,107,834 |
Ideker , et al. |
April 28, 1992 |
Low energy multiple shock defibrillation/cardioversion discharge
technique and electrode configuration
Abstract
A cardioversion/defibrillation system employing a dual biphasic
and multi-electrode discharge technique for effectively
defibrillating the heart by creating a voltage gradient throughout
substantially all of the heart which is above a critical voltage
gradient while delivering a minimum energy shock. Effective
cardioversion/defibrillation is accomplished by delivering two
shocks to the heart. The first shock is at an energy level lower
than that typically necessary to cardiovert/defibrillate the heart
alone, and is applied between a first pair of
cardioversion/defibrillation electrodes. The second shock is at an
energy less than the first shock and is applied between a second
pair of electrodes to shock the area of the myocardium provided
with an inadequate voltage gradient from the first shock. The
voltage gradient in the low gradient areas is boosted above the
minimum gradient necessary to defibrillate. Thus, substantially the
entire myocardium is depolarized by a voltage gradient above the
critical voltage gradient, but with the total shock strength of the
first and second shocks being substantially reduced.
Inventors: |
Ideker; Raymond E. (Durham,
NC), Guse; Paul A. (Durham, NC), Lang; Douglas J.
(Arden Hills, MN), Swanson; David K. (Roseville, MN),
Dahl; Roger W. (Andover, MN) |
Assignee: |
Cardiac Pacemakers, Inc. (St.
Paul, MN)
|
Family
ID: |
24597804 |
Appl.
No.: |
07/647,658 |
Filed: |
January 30, 1991 |
Current U.S.
Class: |
607/5 |
Current CPC
Class: |
A61N
1/3918 (20130101) |
Current International
Class: |
A61N
1/39 (20060101); A61N 001/39 () |
Field of
Search: |
;128/419D |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Kamm; William E.
Assistant Examiner: Getzow; Scott M.
Attorney, Agent or Firm: Fleit, Jacobson, Cohn, Price,
Holman & Stern
Claims
We claim:
1. A system for cardioverting/defibrillating the heart of a patient
comprising:
arrhythmia detection means for detecting the occurrence of an
arrhythmia;
capacitor means for storing electrical energy to be discharged to
the heart;
a first pair of discharge electrodes implanted on or about the
heart for discharging through the heart;
a second pair of discharge electrodes implanted on or about the
heart for discharging through a local region of the heart known to
experience a low local voltage gradient in a known discharge
distribution resulting from discharge of the first pair of
discharge electrodes;
means for charging the capacitor means to a voltage level;
circuit means connected to the capacitor means for discharging the
capacitor means to generate first and second defibrillation pulses,
the first defibrillation pulse being of a higher level than the
second defibrillation pulse; and
switch means connected to the circuit means and each of said
discharge electrodes for delivering the first defibrillation pulse
to the heart via the first pair of discharge electrodes and
delivering the second defibrillation pulse to the heart via the
second pair of discharge electrodes.
2. The system of claim 1, wherein said circuit means generates said
first defibrillation pulse at an energy level which is lower than
that necessary to cardiovert/defibrillate the heart alone.
3. The system of claim 2, wherein said switch means is programmable
to deliver said second defibrillation pulse to said second pair of
discharge electrodes subsequent the delivery of the first
defibrillation pulse to the first pair of discharge electrodes.
4. The system of claim 2, wherein the first pair of discharge
electrodes comprises a first electrode implanted in the right
atrium and a second electrode implanted in the right ventricle, and
the second pair of discharge electrodes comprises a first electrode
positioned on the ventricular apex and a second electrode
positioned in the right ventricular outflow tract.
5. The system of claim 1, wherein said circuit means is a
multi-phasic circuit for producing said first and second
defibrillation pulses as first and second biphasic defibrillation
pulses.
6. The system of claim 5, wherein said multi-phasic circuit
provides a predetermined period of time separating the first
biphasic defibrillation pulse and the second biphasic
defibrillation pulse.
7. The system of claim 5, wherein said multi-phasic circuit means
provides a predetermined period of time between each phase of the
first and second biphasic defibrillation pulses.
8. The system of claim 1, wherein the first pair of discharge
electrodes comprises a first electrode positioned in the right
ventricle and a second electrode positioned subcutaneously in the
body of the patient outside the thoracic cavity, and the second
pair of discharge electrodes comprises a first electrode implanted
on the ventricular apex and a second electrode positioned in the
right ventricular outflow tract.
9. The system of claim 1, wherein the first pair of discharge
electrodes comprises a first electrode positioned in the right
ventricle and a second electrode positioned subcutaneously in the
body of the patient outside the thoracic cavity, and the second
pair of discharge electrodes comprises a first electrode implanted
on the ventricular apex and a second electrode positioned in the
coronary sinus.
10. The system of claim 1, wherein the first pair of discharge
electrodes comprises a first electrode implanted in the superior
vena cava and a second electrode implanted in the right ventricle,
and the second pair of discharge electrodes comprises a first
electrode positioned on the ventricular apex and a second electrode
positioned in the right ventricular outflow tract.
11. The system of claim 1, wherein both electrodes of the first
pair of discharge electrodes and one of the electrodes of the
second pair of discharge electrodes are supported by a single
intravascular catheter lead.
12. The system of claim 1, wherein said capacitor means is a single
capacitor.
13. A method for cardioverting/defibrillating the heart of a
patient comprising the steps of:
implanting a first pair of electrodes on or about the heart for
discharging through the heart;
implanting a second pair of electrodes on or about the heart for
discharging through a local region of the heart known to experience
a low local voltage gradient in a known discharge distribution
resulting from the discharge of the first pair of discharge
electrodes;
charging a capacitor to a voltage level;
discharging the capacitor to generate first and second
defibrillation pulses, the first defibrillation pulse being of a
higher level than the second defibrillation pulse; and
delivering the first defibrillation pulse to the heart via the
first pair of electrodes and delivering the second defibrillation
pulse to the heart via the second pair of electrodes.
14. The method of claim 13, wherein the known discharge
distribution resulting from the first pair and second pair of
discharge electrodes is determined through mapping studies.
15. The method of claim 13, wherein the step of discharging the
capacitor to generate said first and second defibrillation pulses
generates such pulses as first and second biphasic defibrillation
pulses.
16. The method of claim 15, and further comprising the step of
providing a period of time between the beginning of the second
biphasic defibrillation pulse and the end of the first biphasic
defibrillation pulse.
17. The method of claim 15, and further comprising the step of
providing a period of time between each phase of said first and
second biphasic defibrillation pulses.
18. The method of claim 13, and further comprising the step of
providing a period of time between the beginning of the second
defibrillation pulse and the end of the first defibrillation
pulse.
19. A system for cardioverting/defibrillating the heart of a
patient comprising:
arrhythmia detection means for detecting the occurrence of an
arrhythmia;
capacitor means for storing electrical energy to be discharged to
the heart;
a first discharge electrode implanted in the right ventricular
region of the heart;
a subcutaneous patch electrode implanted outside the thoracic
cavity;
a second discharge electrode implanted on the ventricular apex of
the heart;
a third discharge electrode implanted in the right ventricular
outflow tract of the heart;
means for charging the capacitor means to a voltage level;
circuit means connected to the capacitor means for discharging the
capacitor means to generate first and second biphasic
defibrillation pulses, the first biphasic defibrillation pulse
being of a higher level than the second biphasic defibrillation
pulse but lower than that necessary to cardiovert/defibrillate the
heart alone; and
switch means connected to the circuit means and each of said
discharge electrodes and subcutaneous patch electrode for
delivering the first biphasic defibrillation pulse to the heart
between the first discharge electrode and the subcutaneous patch
electrode and delivering the second biphasic defibrillation pulse
to the heart between the second discharge electrode and the third
discharge electrode.
20. A system for cardioverting/defibrillating the heart of a
patient comprising:
arrhythmia detection means for detecting the occurrence of an
arrhythmia;
capacitor means for storing electrical energy to be discharged to
the heart;
a first pair of discharge electrodes implanted on or about the
heart for discharging through the heart;
a second pair of discharge electrodes implanted on or about the
heart for discharging through a local region of the heart known to
experience a low local voltage gradient in a known discharge
distribution resulting from discharge of the first pair of
electrodes;
means for charging the capacitor means to a voltage level;
multi-phasic circuit means connected to the capacitor for
discharging the capacitor to generate first and second biphasic
defibrillation pulses, the first biphasic defibrillation pulse
being of a higher level than the second biphasic defibrillation
pulse but lower than that necessary to cardiovert/defibrillate the
heart alone; and
programmable switch means connected to the multi-phasic circuit
means and each of said discharge electrodes for delivering the
first biphasic defibrillation pulse to the heart via the first pair
of discharge electrodes and delivering the second biphasic
defibrillation pulse to the heart via the second pair of discharge
electrodes.
21. The system of claim 20, wherein said multi-phasic circuit
provides a predetermined period of time separating the first
biphasic defibrillation pulse and the second biphasic
defibrillation pulse.
22. The system of claim 20, wherein said multi-phasic circuit means
provides a predetermined period of time between each phase of the
first and second biphasic defibrillation pulses.
23. A system for cardioverting/defibrillating the heart of a
patient comprising:
arrhythmia detection means for detecting the occurrence of an
arrhythmia;
a capacitor for storing electrical energy to be discharged to the
heart;
an intravascular catheter lead inserted through the vena cava of
the heart and supporting a first discharge electrode positioned in
the superior vena cava, a second discharge electrode positioned in
the right ventricle and a third discharge electrode positioned
within the right ventricular outflow tract;
a fourth discharge electrode implanted on the ventricular apex;
means for charging the single capacitor to a voltage level;
multi-phasic circuit means connected to the single capacitor for
generating first and second biphasic defibrillation pulses, the
first biphasic defibrillation pulse being of a higher level than
the second biphasic defibrillation pulse but lower than that
necessary to cardiovert/defibrillate the heart alone; and
programmable switch means connected to the multi-phasic circuit
means and each of said discharge electrodes and subcutaneous patch
electrode for delivering the first biphasic defibrillation pulse to
the heart between the first discharge electrode and the second
discharge electrode and delivering the second biphasic
defibrillation pulse to the heart between the third discharge
electrode and the fourth discharge electrode.
Description
BACKGROUND OF THE INVENTION
The present invention relates to implantable defibrillation
systems, and more particularly to an implantable defibrillation
system which employs a multiple electrode configuration and
requires lower energies to defibrillate a heart.
There is a continuing effort in the field of implantable
cardioversion/defibrillation to minimize the energy required to
effectively cardiovert/defibrillate a patient's heart. Some of this
effort has focused on the structure and placement of
cardioversion/defibrillation electrodes to maximize the efficiency
with which energy is delivered to the heart and to minimize the
complexity of the surgical procedure required to implant or
otherwise place the electrodes in or about the heart.
For example, U.S. Pat. No. 4,827,932 to Ideker et al. relates to
epicardial implantable defibrillation patch electrodes. A first
patch is designed to fit over the right ventricle and a second
patch is designed to fit over the left ventricle with a
substantially uniform gap being provided between borders of the
patches. The gap is of sufficient width to prevent shunting of
current between the two patches. The electrodes disclosed in this
patent are described as achieving a uniform voltage gradient
throughout the entire ventricular mass.
As another example, U.S. Pat. No. 4,603,705 to Speicher et al.
discloses an intravascular multiple electrode catheter for
insertion into the heart through the superior vena cava. The
catheter supports a distal electrode for sensing and pacing, an
intermediate electrode for sensing, pacing and cardioverting, and a
proximal electrode for sensing and cardioverting. A patch electrode
may be used in conjunction with the catheter.
Other efforts have been directed to particular types of
cardioversion/defibrillation waveforms and techniques for
delivering the waveforms to the heart. For example, U.S. Pat. Nos.
4,637,397 to Jones et al., 4,800,883 to Winstrom, and 4,821,723 to
Baker, Jr. et al. are representative of patents disclosing systems
and techniques for generating multi-phasic defibrillation
waveforms. Another defibrillation waveform variation is disclosed
in U.S. Pat. No. 4,768,512 to Imran which relates to a
high-frequency truncated exponential waveform.
Elaborate defibrillation delivery techniques have been developed in
an attempt to minimize the energy required by providing uniform
voltage gradients throughout the myocardium. U.S. Pat. Nos.
4,548,203 and 4,708,145 to Tacker, Jr. et al., and U.S. Pat. Nos.
4,641,656 and 4,774,952 to Smits disclose a sequential orthogonal
pulse delivery regime in which two pairs of opposing electrodes are
implanted orthogonally to each other. A first shock is delivered
between the first pair of electrodes and a second shock is
delivered between the second pair of electrodes. This technique is
described in these patents as equalizing the current distribution
across the heart and concentrating the current in the muscular
areas of the heart.
Yet another variation of the aforementioned systems is that
disclosed in U.S. Pat. No. 4,727,877 to Kallok. The Kallok patent
discloses a transvenous defibrillation lead system including a
first catheter supporting a first electrode pair comprising a right
apex ventricular electrode and a superior vena cava electrode. A
second electrode pair is provided, comprising a ventricular tip
electrode at the end of the first catheter and a coronary sinus
electrode supported by a transvenous superior vena cava right
atrial lead. A first pulse is delivered to the first pair of
electrodes between the ventricular apex and the vena cava, and a
preset time interval later, a second pulse is delivered to the
second pair of electrodes between the ventricular apex and the
coronary sinus. The patent states that a spatial summation of the
sequential shocks occurs resulting in a reduction of the energy
required to defibrillate the heart as compared to prior
systems.
Rather than attempt to achieve uniform gradients throughout the
myocardium, a technique has been developed which ensures that
substantially all of the myocardium is placed above a critical
voltage gradient so as to effectively countershock a fibrillating
heart at low energies.
SUMMARY OF THE INVENTION
In brief, the present invention is directed to a
cardioversion/defibrillation electrode configuration and discharge
technique in which cardioversion/defibrillation is achieved with
minimal voltage and energy. It is the desire to defibrillate the
heart by creating a voltage gradient throughout substantially all
of the heart which is above a critical voltage gradient while
delivering a minimum energy shock. Effective
cardioversion/defibrillation is accomplished with the present
invention by delivering two shocks to the heart. When a shock is
delivered to the heart, certain regions of the heart are
defibrillated while other regions may not be defibrillated. The
defibrillated regions are boosted to or above a defibrillation
threshold voltage. These regions are hereinafter referred to as
high voltage gradient regions. Conversely, the non-defibrillated
regions are not boosted to the defibrillation threshold and are
hereinafter referred to as low voltage gradient regions. In the
present invention, the first shock can be at an energy level lower
than that typically necessary to cardiovert/defibrillate the entire
heart, and is applied between a first pair of
cardioversion/defibrillation electrodes. The second shock is at an
energy less than the first shock and is applied between a second
pair of electrodes to depolarize a particular area of the
myocardium experiencing a low voltage gradient resulting from the
first shock. Consequently, upon the delivery of the second shock,
the voltage gradient in any low gradient areas resulting from the
first shock is boosted above the minimum gradient necessary to
defibrillate. In effect, the majority of the heart (high voltage
gradient regions) is defibrillated with the first shock delivered
by the first pair of electrodes and the remainder of the heart (low
voltage gradient regions) is defibrillated with the second shock
delivered by the second pair of electrodes.
Unlike the prior systems which attempt to achieve uniform voltage
gradients through spatial summation of shocks, the present
invention accepts non-uniformity and uses it as an advantage to
defibrillate the heart with an overall lower energy. Thus,
substantially the entire myocardium is depolarized by a voltage
gradient above the critical voltage gradient, but with the total
shock strength of the first and second shocks being substantially
reduced.
According to a preferred embodiment of the present invention, the
first and second shocks are biphasic cardioversion/defibrillation
waveforms. However, the first and second shocks may be any type of
defibrillation shock. A time interval may be provided between the
termination of the first shock and the initiation of the second
shock, and also between the phases of each biphasic shock. The
entire shock cycle can be generated with a single capacitor since
the second shock is at lower voltage and energy than the first. By
using a single capacitor, energy that is otherwise left in the
capacitor after discharge and thus wasted, is instead being used
for the second shock in accordance with the present invention.
The electrode configuration used in accordance with the present
invention is designed to maximize efficacy. Specifically, the
electrode configuration consists primarily of a catheter electrode
inserted through the superior vena cava to the right ventricle,
supporting electrodes positioned in the superior vena cava, right
ventricle and right ventricular outflow tract. A subcutaneous
patch, coronary sinus electrode or left ventricular apical patch
electrode may be provided to be discharged against one of the
catheter electrodes.
It is a primary object of the present invention to
cardiovert/defibrillate the heart at lower energies and without
concern for the uniformity of the voltage gradient created across
the heart by a cardioversion/defibrillation waveform.
The above and other objects and advantages will become more readily
apparent when reference is made to the following description taken
in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic diagram illustrating the low energy
defibrillation/cardioversion system according to the present
invention.
FIG. 2 is a schematic view of a single lead supporting multiple
electrodes used in accordance with the present invention.
FIGS. 3A-3C are graphic plotdiagrams of
defibrillation/cardioversion waveforms used in the
defibrillation/cardioversion system of the present invention.
DETAILED DESCRIPTION OF THE DRAWINGS
Referring first to FIG. 1, the defibrillation/cardioversion system
according to the present invention is shown generally comprising an
electronic circuitry portion 10 and an implantable lead
configuration 12. The electronic circuitry portion 10 is
implantable and comprises several components well known in the art.
Specifically, an ECG amplifier 14 is provided for amplifying sensed
cardiac signals. The amplified cardiac signals are fed to an
arrhythmia detector 16 which analyzes the electrical cardiac
activity and determines if and what type of arrhythmia exists. The
arrhythmia detector 16 may be one of several types known in the art
and preferably is capable of distinguishing between high rate
malignant tachycardias and ventricular fibrillation so as to
deliver lower energy shocks in the former case than those to be
delivered in the latter case. A capacitor charging circuit 18 (also
known as an invertor circuit) is provided which in response to the
arrhythmia detector, supplies a charging current to the capacitor
20 connected thereto.
The discharge of the capacitor 20 is controlled by a multi-phasic
circuit 22. The biphasic pulse generating circuit disclosed in U.S.
Pat. No. 4,850,357 may, for example, be used as the multi-phasic
circuit 22. The capacitor 20 is connected to a programmable switch
24 which controls the destination of the defibrillation waveform
generated by the multi-phasic circuit 22 in conjunction with the
capacitor 20. The programmable switch 24 is connected to each of
the electrodes shown in FIG. 1 forming part of the electrode
configuration 12.
The electrode configuration 12 is a substantially non-thoracotomy
multi-electrode configuration or multiple single electrode lead
system as known in the industry. Four catheter mounted electrodes
are provided, one catheter supporting a distal electrode positioned
in the right ventricular outflow tract (OT), a proximal electrode
positioned in the superior vena cava (SVC) or right atrium (RA)
(not shown) and an intermediate electrode positioned in the right
ventricular apex (RV). As shown in FIG. 2, the SVC or RA, RV and OT
electrodes may be supported on a single intravascular catheter
lead. The SVC or RA electrodes are positioned on a more proximal
portion of the catheter lead body 30. The RV and OT electrodes are
positioned on opposite sides of a J-shaped bend 32 at the distal
end of the lead body. Each of the electrodes is connected through
separate electrical conductors (contained within the catheter lead
body 30) to the programmable switch 24. Furthermore, a sensing ring
34 is provided at the distal end of the catheter lead body 30 for
sensing the electrical activity of the heart.
A second lead is inserted into the coronary sinus and supports an
electrode (CS). This lead is a small diameter single chamber
defibrillation catheter lead minus a pacing tip, or may be a narrow
patch electrode. The non-catheter electrodes may include one or
both of an apical patch electrode (A) mounted over the left
ventricular apex and a subcutaneous patch electrode (P) positioned
beneath the skin outside the thoracic cavity. Each of the
electrodes shown in FIG. 1 is connected to the programmable switch
24. Placement of the electrodes is an important aspect of the
present invention.
Electrode placement preferably is determined in the laboratory by
mapping studies, which can provide general information about the
overall typical patient population. Such generalized mapping
studies are performed to determine typical voltage gradients across
the myocardium in response to various electrode shock
configurations, and hence, to show preferred electrode
configuration and placement outside the operating room. This
procedure is described in more detail in an article by Tang et al.
entitled "Measurement of Defibrillation Shock Potential
Distributions and Activation Sequences of the Heart in Three
Dimensions", Proceedings of IEEE, vol. 76, 1988, pages 1176-1186.
Recording electrodes or probes are inserted into the atria,
ventricles and intraventricular septum to record from many sites
(e.g. 128) throughout the heart. A shock is delivered to the heart
between a pair of electrodes. The signals from the recording
electrodes are routed to a computer assisted mapping system capable
of processing the 128 channels simultaneously. Computer assisted
mapping is known in the art. See, for example, the article to Smith
et al. entitled "Computer Techniques for Epicardial and Endocardial
Mapping", Progress of Cardiovascular Discovery, vol. 26, 1983,
pages 15-32. The localized potential gradients from the shock
between electrode pairs are calculated by a method developed by
Clayton et al. and described in his article entitled "Measured and
Calculated Epicardial Potentials and Gradients Resulting From
Transthoracic Stimulation", 1987 Ph.D. Dissertation, Duke
University, Durham, N.C.
The mapping studies are performed on representative patients (or
animals) to determine, as an average, the localized high and low
voltage gradient regions resulting from the discharge between the
pair of electrodes in the mapping study. On the basis of these
mapping studies, and according to the present invention, a first
pair of electrodes is implanted on or about the heart for
discharging substantially throughout all of the heart. A second
pair of electrodes is implanted on or about the heart for
discharging through the local region of the heart corresponding to
the expected low voltage gradient area resulting from the shock
between the first pair of electrodes, as determined from the
mapping studies. Thus, the positions of both pairs of electrodes
are determined from the mapping studies. (The term "on or about the
heart" is meant to include on the surface, in the region such as
subcutaneously, and within the heart.) In other words, the first
pair of electrodes is implanted and will have associated therewith
regions of high and low localized voltage gradients resulting from
discharge therebetween. The second pair of electrodes is implanted
to capture (raise above a critical defibrillating threshold) the
localized low gradient areas with respect to the discharge
distribution of the first pair of electrodes. It is to be
understood that the term "pair" can be generalized to mean "set";
that is, more than two electrodes.
According to the present invention, the programmable switch 24
controls the destination of each phase of the waveform generated by
the multi-phasic circuit 22 and discharged by the capacitor 20 so
that the electrodes of a first pair (or combination) of the
electrodes are discharged against each other during a first
biphasic shock and the electrodes of a second pair or combination
of electrodes are discharged against each other during a second
biphasic shock. It is known that an arrhythmic heart can be
defibrillated if substantially all of the heart is above a critical
voltage gradient. However, non-uniformity in the voltage gradient
throughout the heart created by the fields developed between the
shocking electrodes is accepted and actually used as an advantage
in accordance with the present invention. That is, the first shock
between the first pair of electrodes creates regions in the heart
where the current density is higher than that in others; and the
first shock therefore captures (defibrillates) certain areas of the
myocardium experiencing high (i.e., above threshold) current
density as a result of the first shock, while failing to capture
other predictable areas of the myocardium experiencing low (i.e.,
below threshold) voltage gradients. Through the mapping studies,
the localized low voltage gradient areas are known relative to the
configuration and placement of the first pair of discharging
electrodes. The second shock can, therefore, be at a lower energy
by delivering the second shock between the second pair of
electrodes which are positioned to deliver energy mainly to the
localized low voltage gradient areas not captured by the first
shock delivered between the first pair of electrodes. As a result,
the overall energy of the first and second shocks can be lowered
substantially, while still creating voltage gradients throughout
the heart which are above threshold and hence will convert the
arrhythmia.
Shown in FIG. 3A is a dual biphasic waveform used in conjunction
with the electrode configuration shown in FIG. 1. The first shock
(Shock 1) reaches a higher voltage than the second shock (Shock 2)
but is still lower than that necessary to cardiovert the heart
alone. Several discharge sequences are possible with the electrode
configurations shown in FIG. 1. Set forth below is a table
illustrating possible combinations used in dogs. In this example,
the subcutaneous patch P has a surface area of 41 sq. cm. and the
apical electrode A has a surface area of 4.3 sq. cm. The single
biphasic waveform used for a comparison with the dual biphasic
waveforms was 5.5 msecs for each phase. The dual biphasic waveforms
are 3.5 msecs for the first phase and 2 msecs for the second phase.
A single 150 microfarad capacitor was used in this experiment.
______________________________________ DUAL BIPHASIC WAVEFORMS
SHOCK 1/SHOCK 2 1/2 1/2 1/2 DFT RV-P RV-P/A-OT RV-P/A-CS
SVC-RV/A-OT ______________________________________ VOLTS 377 208
258 239 JOULES 9.4 2.7 4.4 3.9 AMPS 5.2 2.7 3.5 4.0
______________________________________
It is readily seen from this table that the dual biphasic waveforms
produce a significantly lower defibrillation threshold (DFT) than a
single biphasic waveform.
FIG. 3B illustrates another type of dual biphasic waveform in
accordance with the present invention. This waveform includes a
programmable time delay t1 and t2 between the phases of each
biphasic portion. It has been found that a biphasic waveform with a
delay of a few milliseconds, for example 2-6 milliseconds, provides
for an effective defibrillation waveform.
FIG. 3C illustrates yet another type of dual biphasic waveform in
accordance with the present invention. A time programmable time
interval t3 is provided between the biphasic shocks. It has been
found that an interval in the range of 1-10 milliseconds provides
an effective defibrillation waveform.
Each of the waveforms shown in FIGS. 3A-3C is generated from the
exponentially decaying voltage envelope E of a single capacitor. As
a result, the second shock, shock 2 (which is desirably lower in
voltage and energy) is a natural consequence of the discharge
voltage waveform of the capacitor. Essentially, the charge
remaining on the capacitor after the first shock is used for the
second shock. There is, therefore, no need to charge another
capacitor or recharge the same capacitor for the second shock.
Rather, the energy used to generate the first and second shocks can
be developed from the same capacitor, being discharged once, with
minimal waste of energy that would normally remain in the
capacitor. Finally, it is considered within the spirit and scope of
the present invention to employ the present inventive technique
with any type of defibrillation pulse whereby the first pulse
delivered to the first pair of electrodes is of greater energy than
the second pulse delivered to the second pair of electrodes.
The above description is intended by way of example only and is not
intended to limit the present invention in any way except as set
forth in the following claims.
* * * * *